1. Field of the Invention
The present invention relates to an interface control method and apparatus for exchanging various kinds of signals between apparatuses or between units.
2. Description of the Related Art
FIG. 2 is a diagram illustrating standard interfaces in an ordinary computer, serving as an information processing apparatus. In FIG. 2, reference numeral 201 represents a PCI (peripheral component interconnect) bus, serving as an internal bus as well as a bus for external expansion. Reference numeral 202 represents a line for a network conforming to Ethernet interface specifications. An SCSI (small computer system interface) interface bus 203 is mainly used for transferring large-capacity data from a hard disk, a CD-ROM (compact disk-read-only memory) or the like. An ISA (industry standard architecture) bus 204 serves as a bus for external expansion. An interface bus 205 connects a graphic controller to a CRT (cathode-ray tube) or a flat-type display, such as an FLCD (ferroelectric liquid crystal display) or the like. Currently, analog interfaces are mainly used. However, digital interfaces using LVDS (low voltage differential signaling) or the like have alreadly been manufactured, and standardization for such digital interfaces will be realized in the near future.
The use of such standardized interfaces has the merit that different apparatuses can be connected and operated compatibly even if they are designed and manufactured by different manufacturers.
However, in order to obtain this benefit, an apparatus must be designed and manufactured so as to conform to the standardized use of interfaces. Accordingly, there is no possibility of adopting original specifications without sacrificing the benefit of stadardization. This results in restriction in the degree of freedom in design, and redards the development of new devices.
When constructing an interface conforming to respective interface specifications, and connecting an apparatus which uses a bus structure such that addresses, data, commands and the like are transmitted using individual signal lines, via the interface, it is usually necessary to connect all of the signal lines. For example, in an apparatus which uses buses having capacities of 26 bits for addresses, 16 bits for data, and a plurality of other control signal lines, such as a PC (personal computer) card, the number of signal lines necessary for the interface is 42 just for addresses and data, and is therefore very large. As the number of bits for addresses and data increases in accordance with an increase in the capacity of data stored in memory or the like, an increase in the number of signal lines requires an increase in the size of cables and connectors. This is a serious problem.
The present invention has been made in consideration of the above-described problems.
It is an object of the present invention to provide an interface control method and apparatus which can newly exchange other data and control signals while conforming to existent interface specifications.
It is another object of the present invention to provide an interface control method and apparatus which can exchange various kinds of signals by superposing a desired signal without influencing existent interface signals.
It is still another object of the present invention to provide an interface control method and apparatus which can reduce the number of used signal lines without reducing the functions of interfaces.
According to one aspect, the present invention which achieves these objectives relates to an interface control apparatus comprising a plurality of transmission channels each including at least a pair of signal lines for transmitting an interface signal, transmission means for transmitting signals via the transmission channels, reception means for receiving the signals so transmitted, modulation means for modulating a desired signal with a high-frequency signal and providing the modulated signal to a signal line of one of the transmission channels, and demodulation means for extracting the modulated signal from that signal line and demodulating the extracted signal.
According to another aspect, the present invention which achieves these objectives relates to an interface control method comprising the steps of modulating a desired signal with a high-frequency signal, supplying the resulting modulated signal to a signal line of one of a plurality of transmission channels each of which includes at least a pair of signal lines for transmitting an interface signal, and extracting the modulated signal from that signal line and demodulating the extracted signal.
According to still another aspect, the present invention which achieves these objectives relates to an interface control apparatus for exchanging signals between a host apparatus and a peripheral apparatus via a plurality of signal lines. The host apparatus comprises address gate means for gating an address signal, and data gate means for controlling a direction of transmission and passage of a data signal whose bits are smaller in number than the bits of the address signal. The peripheral apparatus comprises gate means for inputting the address signal from the host apparatus via a transmission bus having a bus width corresponding to a bus width for the data signal, input gate means for inputting the data signal from the transmission bus, and output gate means for outputting the data signal to the transmission bus. The interface control apparatus comprises control means for outputting a gate control signal for each of the address gate means, the data gate means, the gate means, the input gate means and the output gate means based on a provided access command.
According to yet another aspect, the present invention which achieves these objectives relates to an interface control method for exchanging signals between a host apparatus and a peripheral apparatus via a plurality of signal lines. The method comprises the step of gating an address signal output from the host apparatus by a gate circuit, and inputting/outputting a data signal including bits whose number is smaller than a number of bits of the address signal through a data gate for controlling a direction of transmission and passage of the data gate. The peripheral apparatus inputs the address signal from the host apparatus via a transmission bus having a bus width corresponding to a bus width of the data signal to gate the input address signal and exchanges data with the transmission bus via an input/output gate, outputs a gate control signal for each of the gate circuit, the data gate, and the gate and the input/output gate of the peripheral apparatus based on a provided memory access command, and exchanges the data signal and the address signal via the transmission bus.
The high-frequency signal used for the mentioned modulation should be sufficiently high to avoid influencing nearby circuits, and preferably should be at least 50 to 100 times the frequency of the data signal.
The foregoing and other objects, advantages and features of the present invention will become more fully apparent from the following detailed description of the preferred embodiments taken in conjunction with the accompanying drawings.